The present invention relates to a signal processing circuit, and more particularly, to a signal processing circuit for mitigating pulling effect, and an associated method.
In a traditional transmitter system, a local oscillator (LO) signal is needed for up-converting a baseband signal (a data signal to be transmitted) to generate an up-converted signal such as a radio frequency (RF) signal. When a frequency FLO of the LO signal is obtained by dividing a frequency FVCO of a voltage controlled oscillator (VCO) signal with a frequency dividing factor of 2 (i.e. FLO=FVCO/2), a second harmonic of the up-converted signal will have a frequency that is twice the fundamental frequency of the up-converted signal and is close to the frequency FVCO of the VCO signal. As a result, the second harmonic of the up-converted signal may affect the VCO signal through magnetic coupling between a transformer in the transmitter system (e.g. a balun (balanced-to-unbalanced) transformer) and an inductor of the VCO. Due to this pulling effect, the VCO signal may not be the required perfect sine wave and may cause Error Vector Magnitude (EVM) degradation.
Thus, there is a need for an innovative design capable of effectively mitigating the pulling effect to ensure the signal transmission quality.